A clean and simple brushed metal theme for Firefox Quantum:
https://addons.mozilla.org/en-US/firefox/addon/my-brushed-metal/

Download Classic CSS tweaks for Firefox Quantum:
https://github.com/Aris-t2/CustomCSSforFx/releases/

More Firefox Tweaks - https://winaero.com/blog/category/firefox/

9 Extensions I use for Firefox Quantum:

F.B Purity - https://www.fbpurity.com/install.htm
Google search link fix - https://addons.mozilla.org/en-US/firefox/addon/google-search-link-fix/
Open in MS Edge - https://addons.mozilla.org/en-US/firefox/addon/open-in-microsoft-edge-browser/
RusVPN - https://addons.mozilla.org/en-US/firefox/addon/rusvpn-free-vpn/
Show/Hide Passwords - https://addons.mozilla.org/en-US/firefox/addon/showhide-passwords/
uBlock Origin - https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/
Webmail Ad Blocker - https://addons.mozilla.org/en-US/firefox/addon/webmail-ad-blocker/
YT Anno. No More - https://addons.mozilla.org/en-US/firefox/addon/youtubes-annotations-no-more/
Zoom Image - https://addons.mozilla.org/en-US/firefox/addon/zoom-image/

Software I use on Windows 10 PCs:

7-Zip - http://www.7-zip.org/
Adobe Flash Player - https://helpx.adobe.com/flash-player/kb/installation-problems-flash-player-windows.html
AS SSD Benchmark - http://www.majorgeeks.com/files/details/as_ssd_benchmark.html
ATTO Disk Benchmark - http://www.majorgeeks.com/files/details/atto_disk_benchmark.html 
Audacity - http://www.audacityteam.org/download/windows/
Autoruns - https://technet.microsoft.com/en-us/sysinternals/bb963902
CCleaner - https://www.piriform.com/ccleaner/builds
CPU-Z - http://www.cpuid.com/softwares/cpu-z.html
Crystal Disk Info - http://crystalmark.info/download/index-e.html
Everything Search - https://www.voidtools.com/ 
Firefox - https://ftp.mozilla.org/pub/firefox/releases/
Foobar2000 - http://www.foobar2000.org/download
GPU-Z - https://www.techpowerup.com/download/techpowerup-gpu-z/
HW Monitor - http://www.cpuid.com/softwares/hwmonitor.html 
Malwarebytes - https://www.malwarebytes.org/mwb-download/
Media Player Classic - https://www.videohelp.com/software/MPC-BE
Media Preview - http://babelsoft.net/products/mediapreview.htm
Mp3tag - http://www.mp3tag.de/en/download.html
OldNewExplorer - https://msfn.org/board/topic/170375-oldnewexplorer-119/ 
Open Broadcaster Software - https://github.com/jp9000/obs-studio/releases
Open Shell Menu - https://github.com/Open-Shell/Open-Shell-Menu/releases 
Oracle VM VirtualBox - https://www.virtualbox.org/wiki/Downloads
Orban Loudness Meter - https://www.orban.com/meter/
Share Mouse - http://www.keyboard-and-mouse-sharing.com/download.php
Stereo Tool - http://www.stereotool.com/download/
TeamViewer - https://www.teamviewer.com/en/download/windows/
Thunderbird - https://ftp.mozilla.org/pub/thunderbird/releases/
VLC Media Player -  http://www.videolan.org/vlc/download-windows.html
Winaero Tweaker -  http://winaero.com/blog/category/winaero-tweaker/

Scripts I use for Windows 10 :

Boot Speed file name: bootspeed.vbs

Option Explicit
On Error Resume Next
Dim Wsh, Time1, Time2, Result, PathFile, MsgResult, MsgA, AppName, KeyA, KeyB, TimeDiff
MsgA = "Please close all running applications and click on OK."
KeyA = "HKEY_CURRENT_USER\Software\RestartTime\"
KeyB = "HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\RestartTime"
AppName = "ReBoot-Time"
Set Wsh = CreateObject("WScript.Shell")
PathFile = """" & WScript.ScriptFullName & """"
Result = wsh.RegRead(KeyA & "Times")
if Result = "" then
MsgResult = Msgbox (MsgA, vbOKCancel, AppName)
If MsgResult = vbcancel then WScript.Quit
Wsh.RegWrite KeyA & "Times", left(Time,8), "REG_SZ"
Wsh.RegWrite KeyB, PathFile, "REG_SZ"
Wsh.Run "cmd /c Shutdown -r -t 00", false, 0
else
Wsh.RegDelete KeyA & "Times"
Wsh.RegDelete KeyA
Wsh.RegDelete KeyB
TimeDiff = DateDiff("s",Result,left(Time,8))
MsgBox "Your computer reboots in " & TimeDiff & " seconds", VbInformation, AppName
end if
wscript.Quit

Clear Event Viewer file name: Clear_Event_Viewer.bat

@echo off
FOR /F "tokens=1,2*" %%V IN ('bcdedit') DO SET adminTest=%%V
IF (%adminTest%)==(Access) goto noAdmin
for /F "tokens=*" %%G in ('wevtutil.exe el') DO (call :do_clear "%%G")
echo.
echo goto theEnd
:do_clear
echo clearing %1
wevtutil.exe cl %1
goto :eof
:noAdmin
exit

Older Firefox Add-Ons:

Adblock Plus - https://addons.mozilla.org/en-US/firefox/addon/adblock-plus/
Always on Top - https://addons.mozilla.org/en-US/firefox/addon/always-on-top/
Open With -  https://addons.mozilla.org/en-US/firefox/addon/open-with/
Ultrawidify - https://addons.mozilla.org/en-US/firefox/addon/ultrawidify/

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